An EPR method has been developed for measuring the volume of a membrane encapsulated space through the use of the spin label TEMPONE and the paramagnetic broadening agent K sub 3 Cr (C sub 2 O sub 4) sub 3. This method is being used to monitor the rate and extent of Ca2 ion-induced fusion of phospholipid vesicles. The effects of various parameters including lipid fluidity and Ca2 ion asymmetry will be assessed. Work on Mn2 ion binding to membrane components will be continued. The characteristics of Mn2 ion binding to free fatty acids incorporated into phospholipid vesicles will be explored. Fatty acid induced H ion and Ca2 ion transport will be investigated.